1. Field of the Invention
The present invention generally relates to apparatuses and methods to extend the clamping capacity of bar clamps. More particularly, the present invention relates to an extension fixture to combine the clamping capacity of a pair of bar clamps.
2. Description of the Related Art
Bar clamps are commonly used in a variety of clamping situations where a clamping force needs to be applied to squeeze two surfaces together. With reference to the figures in which like numerals represent like elements throughout, FIG. 1 is a side perspective view of a commonly available bar clamp 10. A bar clamp 10 is typically comprised of a bar 30, with a fixed jaw 40 at one end, and a movable jaw 50 positioned on the bar. The movable jaw 50 may be slid along the bar 30 to vary the working capacity of the clamp 10. Both the fixed and movable jaws 30, 40 have parallel faces 42, 52 or clamping surfaces, for applying a clamping force to a work piece. The movable jaw 50 has a ratcheting or locking mechanism for restraining the movable jaw body at a position along the bar 30. The movable jaw 50 also has a clamping mechanism 56 for forcing the face 52 of the movable jaw 50 towards the fixed jaw face 42.
As shown in FIG. 2, a bar clamp 10 may be used to provide a clamping force across a single object 14, or multiple objects 14 positioned within the clamp. Bar clamps are especially useful in that they provide a clamping force between the two jaws 42, 52, with the jaws remaining substantially parallel to one another and perpendicular, or at ninety degrees to, the bar 30 as the clamping force is applied. The clamping force is depicted in FIG. 2 by arrows “A.” Another useful feature of a bar clamp 10 is the straight reference edges the upper and lower edges 32, 34 of the bar 30 provides when clamping objects 14 together. For example as depicted in FIG. 2, multiple objects 14 may be positioned against the bar upper edge 32 and thus aligned with one another. To ensure the bar 30 remains straight under the clamping forces “A” the bar has a cross-sectional shape which is configured to resist bending. The straightness of the bar also ensures the fixed and movable jaw faces 42, 52 remain parallel as the clamping force is applied to the work piece.
As further shown in FIG. 2, a clamping force is applied to an object 14, or series of objects, by placing them within the bar clamp 10 between the fixed jaw 40 and the movable jaw 50. The movable jaw 50 is then moved along the bar 30 to initially position the objects 14 to be clamped adjacent the fixed jaw face 42 and movable jaw face 52. The clamping mechanism 56 is then actuated to provide a desired clamping force to squeeze the objects between the fixed jaw face 42 and movable jaw face 52. Typically the movable jaw 50 is readily reversible on the bar 30 with the fixed jaw 40 having a second outward face 44. When the movable jaw is reversed on the bar, the clamping mechanism 56 will force the movable jaw face 52 away from the fixed jaw outward face 44, and thus the bar clamp 10 may provide a spreading force between the fixed jaw outward face 44 and the movable jaw face 52. A bar clamp 10 typically has a hole 92 formed in the end of the bar 30 opposing the fixed jaw 40 which may be used to hang the clamp when stored.
A typical prior art clamping application in which bar clamps would be employed is the forming of a flat panel from multiple boards. As depicted in FIG. 3, a pair of bar clamps 10 may be positioned on a flat reference surface 16. The reference surface 16 then ensures that the upper edges 32 of the bars 30 are coplanar with one another. The upper edges 32 of bars 30 then present a substantially flat surface upon which multiple objects may be positioned to be clamped together. The surfaces of the objects adjacent the bar clamps 10 will then form a substantially flat or coplanar surface with one another. FIG. 3 shows two boards 14, depicted as transparent by dashed lines, being glued and clamped together by the bar clamps 10. In this manner, a flat panel such as a table top comprised of multiple boards 14 may be glued and clamped together while ensuring the surfaces of the boards 14 touching the upper edges 32 of the bar 30 are all substantially coplanar with one another. In this application, the straightness of each bar 30 under a clamping force, the parallel clamping action of the jaw faces 42, 52, and the jaw faces remaining perpendicular to the bar 30 are critical to ensure a completed panel with no bow or twist in the finished surface.
The clamping capacity of any bar clamp is limited by the length of the bar. The movable jaw may be positioned at the end of the bar away from the fixed jaw, which then forms the maximum distance between the fixed and movable jaw faces. This distance is typically referred to as the clamping capacity, or size, of the bar clamp. A craftsman will evaluate the clamping task at hand and selects an appropriate size bar clamp to embrace the work piece.
In practice, having only large capacity clamps is undesirable in that a clamp that is substantially longer than the work piece is ungainly in use. To allow for the efficient clamping various size objects, in a variety of clamping situations, a craftsman is then required to have several bar clamps of varying lengths. Moreover, the price of the bar clamps increases relative to the size of the clamp. The retail price of a bar clamp is proportional to the length of the clamp, with the larger higher capacity clamps being the most expensive. The greatest return for investment in the purchase of clamps is typically achieved by purchasing a series of short and intermediate length clamps to accommodate the bulk of clamping jobs at hand. When a task requires an especially large capacity clamp, a craftsman is forced to either purchase an expensive large capacity clamp, or find another means to clamp the work piece.
One example of a prior art bar clamp extension device is disclosed in U.S. Pat. No. 6,530,565, issued to Simpson. The Simpson extension device comprises an extension bar purchased separately from a bar clamp and a coupler used to join the extension bar to the bar of an existing clamp. In operation, the bar clamp requiring an extended capacity is modified by removing the fixed head from the clamp. The coupler is then used to join the bar of the bar clamp and the extension bar. The fixed head previously removed from the clamp is then placed on the opposing end of the extension bar from the coupler. A major disadvantage of the Simpson device is that it is designed for use on light duty bar clamps having a readily removable fixed head. The fixed head of the majority of heavy duty bar clamps on the market are not designed to be removable. The fixed head in heavy duty clamps is typically permanently secured to the bar by rivets or pins pressed into the assembly and is not designed to be removable by the craftsman in operation. For example, to remove the fixed head from the bar in a riveted design, the rivets must be drilled out of the head and bar. The rivets are thus destroyed in the removal process and must be replaced with another component upon reassembly. In a pin design, the pins must be forcibly driven from the head and bar and are not easily driven or forced back into position to reassemble the clamp. A few examples of such heavy duty clamp designs are marketed under the trade names; Bessey® K-body™, Gross Stabil® PC2™, Jorgenson® Cabinet Master™, and Jet® Parallel Clamps. Another major disadvantage of the Simpson device is that it is designed to extend the reach of light duty bar clamps having a bar of rectangular cross section. All the heavy duty bar clamps above have a bar which uses an I-beam cross section. The I-beam cross section efficiently maximizes the bending stiffness of the bar and is used in most heavy duty clamps.
According, it would be advantageous to provide a device and method to allow the accomplishment of large clamping jobs without the need for the purchase of large capacity heavy duty bar clamps. Such device and method would allow the use of a combination of small or medium capacity heavy duty bar clamps to accomplish a clamping task otherwise requiring a larger capacity clamp. The device and method should also preserve the advantages of bar clamps such as the straight reference edges provided by the bar and the parallel clamping action of the jaws of the clamp. It is thus to such a bar clamp extension device and method that the present invention is primarily directed.